One of the most important interventions for osteoporosis is prevention of bone loss. Regarding prevention strategies, the main emphasis has been on dietary calcium intake, however calcium by itself has limited efficacy. Thus, any component that can improve calcium's effect on bone mass can improve bone health significantly. Conjugated linoleic acid (CLA) may be a good candidate for controlling osteoporosis based on the observation that CLA reduces body fat while increasing lean mass along with total ash. However, the reported effects of CLA on bone mass have not been consistent. We hypothesized that the inconsistency of CLA with regard to bone mass is due to differences in dietary calcium content. The long term goal of this research is to obtain a systematic understanding of how dietary CLA delivered along with dietary calcium can improve bone mass, eventually leading to their use in preventing osteoporosis. The objective of this R21 application is to identify the effect of calcium and ability of CLA to increase calcium's effect on prevention of osteoporosis. Two hypotheses to be tested are (1) CLA improves calcium's effect on bone mass during a bone loss period, and (2) CLA enhances bone mass by improving bone formation while reducing bone marrow adiposity. The rationale for the proposed research is that information from this proposed research will serve as the basis of clinical trials, which can provide critical information regarding the use of CLA supplementation along with calcium for the prevention of osteoporosis. Thus, the proposed research is relevant to that part of NIH's mission that pertains to developing knowledge that will potentially help to reduce human diseases. Based on preliminary data, these hypotheses will be tested by pursuing two specific aims: (1) Determine the interaction between CLA and calcium during a period of bone loss;and (2) Determine key molecular mechanisms of CLA on bone marrow mesenchymal stem cell differentiation. Under the first aim, the interaction between CLA and dietary calcium in ovariectomized mice will be established along with calcium homeostasis and bone physiology to understand the mechanism of interaction between CLA and calcium. Under the second aim, the key molecular mechanisms of CLA on bone marrow adipocyte and bone formation will be identified by two separate approaches;the effects of CLA on bone marrow adipocyte formation (adipogenesis), and on bone formation (osteoblastogenesis) in bone marrow mesenchymal stem cells. This approach is innovated because it uses two functional ingredients'interaction along with bone marrow stem cell differentiation to understand and apply knowledge for prevention of osteoporosis. The Public Health relevance of this project is that, by identifying any dietary components that can improve calcium's benefit on bone health will have a significant impact on reduction and/or prevention of osteoporosis that can lead to an improved quality of life, particularly in the elderly. PUBLIC HEALTH RELEVANCE: Osteoporosis is a disease characterized by low bone mass, with the elderly particularly susceptible, and it affects the quality of life as well as increasing mortality, due to complications. A unique prevention strategy by co-treatment of conjugated linoleic acid and calcium can potentially be a very useful tool for preventing the development of osteoporosis, leading to improved quality of life particularly in the elderly.